/*
 * @description:下雨效果
 */

class RainEffect {
  constructor(viewer, options) {
      if (!viewer) throw new Error('no viewer object!');
      options = options || {};
      //倾斜角度，负数向右，正数向左
      this.tiltAngle = Cesium.defaultValue(options.tiltAngle, -.6);
      this.rainSize = Cesium.defaultValue(options.rainSize, 0.3);
      this.rainSpeed = Cesium.defaultValue(options.rainSpeed, 60.0);
      this.viewer = viewer;
      this.init();
  }

  init() {
      this.rainStage = new Cesium.PostProcessStage({
          name: 'czm_rain',
          fragmentShader: this.rain(),
          uniforms: {
              tiltAngle: () => {
                  return this.tiltAngle;
              },
              rainSize: () => {
                  return this.rainSize;
              },
              rainSpeed: () => {
                  return this.rainSpeed;
              }
          }
      });
      this.viewer.scene.postProcessStages.add(this.rainStage);
  }

  destroy() {
      if (!this.viewer || !this.rainStage) return;
      this.viewer.scene.postProcessStages.remove(this.rainStage);
      this.rainStage.destroy();
      delete this.tiltAngle;
      delete this.rainSize;
      delete this.rainSpeed;
  }

  show(visible) {
      this.rainStage.enabled = visible;
  }

  rain() {
      return "uniform sampler2D colorTexture;\n\
              varying vec2 v_textureCoordinates;\n\
              uniform float tiltAngle;\n\
              uniform float rainSize;\n\
              uniform float rainSpeed;\n\
              float hash(float x) {\n\
                  return fract(sin(x * 133.3) * 13.13);\n\
              }\n\
              void main(void) {\n\
                  float time = czm_frameNumber / rainSpeed;\n\
                  vec2 resolution = czm_viewport.zw;\n\
                  vec2 uv = (gl_FragCoord.xy * 2. - resolution.xy) / min(resolution.x, resolution.y);\n\
                  vec3 c = vec3(.6, .7, .8);\n\
                  float a = tiltAngle;\n\
                  float si = sin(a), co = cos(a);\n\
                  uv *= mat2(co, -si, si, co);\n\
                  uv *= length(uv + vec2(0, 4.9)) * rainSize + 1.;\n\
                  float v = 1. - sin(hash(floor(uv.x * 100.)) * 2.);\n\
                  float b = clamp(abs(sin(20. * time * v + uv.y * (5. / (2. + v)))) - .95, 0., 1.) * 20.;\n\
                  c *= v * b;\n\
                  gl_FragColor = mix(texture2D(colorTexture, v_textureCoordinates), vec4(c, 1), .5);\n\
              }\n\
              ";
  }
}

Cesium.RainEffect = RainEffect;
